1. Field of the Invention
The present invention relates to a probe for inspecting surface anomalies and irregularities of a circumferential slot in a turbojet disk by means of eddy currents.
2. Description of the Related Art
The circumferential slot of a turbojet disk is intended to receive a series of blades and it is subjected to high levels of stress when the turbojet is in operation, in particular on its faces of concave angular shape (referred to below as the “side faces” of the slot). As a result, slots of this type require very regular inspection. Given the poor accessibility of the side faces, it is common practice to verify their surface state by performing inspection by means of eddy currents. This type of inspection consists in scanning the surface for examination by means of a probe fitted with a sensor that, by creating an electromagnetic field, produces eddy currents in the part under inspection. In practice, it is usually the part that is caused to pivot while the probe remains stationary on its support. When the surface of the slot presents anomalies, the eddy current flux is altered and the sensor generates an electrical signal that corresponds to the alteration. The amplitude of the signal is proportional to the magnitude of the detected surface anomaly. In order to ensure that this proportionality remains true, it is nevertheless necessary for contact between the surface for inspection and the eddy current probe to be maintained continuously.
Shoe probes are already known that are made up of a single-element sensor fastened to the end of a stem that is capable of being moved by means of its support along the axial and radial directions of the turbojet disk. That type of probe requires the probe to be moved stepwise along the profile under inspection, each movement of the probe in the axial direction of the disk being followed by a turning movement of the disk or of the probe so as to scan the entire surface of the slot. The single-element sensor is inserted into the slot, put into contact with the surface for inspection, and then the part is caused to perform one complete revolution so that a complete circumferential strip of the slot is examined. That operation is then repeated several times, changing the position of the single-element sensor on the surface for inspection each time so as to scan the entire surface of the slot. Since the single-element sensor is asymmetrical, after one side face of the slot has been inspected, it is necessary to turn the sensor about in order to examine the opposite side. The result enabling the surface state of the slot to be evaluated is obtained by incrementing the results of the various measurement performed using the single-element sensor.
In order to reduce the number of measurements that are needed for a full inspection of the surface of a slot, proposals have been made to replace the single-element sensor of the probe with a multi-element sensor of shape that advantageously matches the profile of one of the side faces of the slot. The entire slot can then be inspected in only two operations (one complete revolution for each side face of the slot, with the sensor being turned around between the two operations).
Those two systems present several drawbacks. The large number of measurements and calculations, and also the difficulty in positioning the sensor against the surface for examination, decrease the accuracy of the results. Furthermore, insofar as the known system allows only one side of the slot to be inspected, problems associated with the stem flexing appear over time, thereby falsifying the measurement results because of the multi-element sensor being poorly oriented relative to the surface for inspection.